The release factor for outgassing of nonradiogenic volatiles (e.g, water) on Mars since the end of accretion and heavy bombardment is estimated to be 0.017--0.112. The estimate is based on the 40Ar release factor (which is 0.012--0.040) and a correction coefficient derived from the history of volcanism on Mars. The 40Ar release factor is calculated from the bulk K content of the planet and its current atmospheric inventory of 40Ar. The range of Martian bulk K contents considered is 150--500 ppm, based on the geochemistry of the shergottites, nakhlites, and Chassigny (SNC) meteorites and the thermal history of the planet. The correction coefficient (termed the nonradiogenic release coefficient) compensates for the variable abundance of 40Ar in the Martian mantle through time versus the relatively constant nonradiogenic volatile abundance and for the variable rate at which outgassing has occurred through time on Mars. Volcanism is used as a measure of outgassing activity, and studies of Martian volcanic activity through time by Greenly (1987) and Tanaka et al. (1988) are used to calculate the correction coefficient. The calculated nonradiogenic relase coefficient are 1.4--2.8; i.e., the release of nonradiogenic volatiles is 1.4--2.8 times the 40Ar release factors. The calculation assumes that Mars has not lost 40Ar since accretion ended and that the nonradiogenic volatiles are released with equal efficiency and by the same events as 40Ar. Interpretation of the results is highly dependent on the fate of early accreted surficial volatiles. If the present atmospheric and surficial volatile inventory is entirely secondary, i.e., released by outgassing after accretion, the release factors calculated may be used as an approximate ratio of present surficial inventory to total volatile content. If Mars retained some primary surficial inventory in addition to secondary volatiles, then the release factors pertain to the secondary fraction only, and estimates of the contribution of volatiles released by volcanism since accretion may be used to constrain the volatile content of the postaccretionary Martian mantle. ¿American Geophysical Union 1990